Technology And Mechanism On Solvent Extraction Of Zinc From High Concentration Zinc Solution By P204

With the continuous mining, the zinc resources couldn't meet the demand. Therefore, the exploitation of low grade zinc ore and secondary zinc resources was imperative. The leaching liquor of low grade zinc ore and secondary zinc residues and secondary zinc wastewater were all with high concentration of zinc and complicated impurities. Solvent extraction of cations was with high selectivity and good separation of impurities. P204 was used extensive on the extraction of zinc, and it was with good effect. When P204 was used as extractant to extract zinc, the pH of extraction system was reduced by the replaced hydrogen ions. When P204 was used to extract zinc from high concentration zinc solution, the pH was decreased substantially, the distribution ratio of extraction equilibrium was influenced obviously, and the extraction rate of zinc was decreased. The method of using alkali to neutralize the hydrogen produced in the process of extraction could improve the extraction rate of zinc. But when the distribution ratio of extraction equilibrium was limited by saturation capacity of organic phase, the pH of extraction system was sharply raised with the overdose of alkali, then emulsification appearred, the viscosity of extraction system was too high to complete extraction. For the emulsification in the process of extraction produced by the slight overdose of alkali, this text studied the method of saponification pretreatment to separate excessive alkali and eliminate emulsification in the process of extraction. The zinc solution with Zn2+concentration of 30g/L was used as research object in this text.This study showed the emulsification was easy to appear in the process of saponification pretreatment caused by the production of surfactant, so that the alkali solution couldn't separate from the organic phase. This text studied kinds of demulsified method, the methods of using a salt compounded with alkali and strong acid or weak acid to demulsify achieved good results. In the case of using a salt compounded with alkali and strong acid to demulsify, a small amount of extractant mixed in the separated aqueous phase, the loss of extractant leaded to the decrease of extraction rate. In the case of using a salt compounded with alkali and weak acid to demulsify, and then using the organic phase to extract zinc, the extraction rate of zinc was relatively enhanced, and there was no emulsification in the process. The main reason was that the salt compounded with alkali and weak acid played two roles, the first one was that the salt could stable the pH of extraction system; the second one was that the weak acid could dissolve in the organic phase, and it could enhance the extraction of zinc, and increase the saturation capacity of P204.In this paper, a systematic research was carried out for enhancing extraction with alkali and weak acid composite additive. The study showed the method of adding alkali and weak acid composite additive into the extraction system derectly and the method of extracting zinc with P204 saponification pretreated by alkali and weak acid composite additive both took with good extraction rate, the single stage extraction rate of zinc was already up to 99.5%, and there was no emulsification in the process of extraction. However, the weak acid consumption was significantly different with two methods. When the concentration of P204 was 40%(1.2mol/L), in the case of extracting zinc by the method of adding alkali and weak acid composite additive derectly, the best extraction rate of 99.61% was got with 80g/L(2mol/L) of alkali consumption and 104mL/L(2mol/L) of weak acid consumption; In the case of extracting zinc with extractant saponification pretreated by alkali and weak acid composite additive, the best extraction rate of 99.9% was got with 48g/L(1.2mol/L) of alkali consumption and 10mL/L(0.2mol/L) of weak acid consumption.In the case of cations co-existing, using P204 as extractant, adding alkali and weak acid composite additive to extraction zinc, the single stage extraction rate was up to 97.84%. The separation of each impurity was higher than 90%, and most of them more than 95%.